Receiving method and apparatus, and communication system using the same

ABSTRACT

A radio unit receives burst signals in a target system or those in a MIMO system. A judgment unit determines if a MIMO signal having a form of channel corresponding to the target system is assigned posterior to a target LTS and a target signal. If a constellation of signal points in a position posterior to the target LTS and target signal corresponds to a constellation of signal points in a MIMO signal, the judgment unit judges that the MIMO signal is assigned in the received burst signal. If it is judged by the judgment unit that the MIMO signal was assigned, an instruction unit stops the operation of a baseband processing unit for MIMO-STS and the like assigned posterior to the MIMO signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to receiving technologies, and itparticularly relates to a receiving method and apparatus, in which burstsignals are received, and a communication system utilizing said methodand apparatus.

2. Description of the Related Art

An OFDM (Orthogonal Frequency Division Multiplexing) modulation schemeis one of multicarrier communication schemes that can realize thehigh-speed data transmission and are robust in the multipathenvironment. This OFDM modulation scheme has been used in the wirelessstandards such as IEEE802.11a and HIPERLAN/2. The burst signals in sucha wireless LAN are generally received via a time-varying channelenvironment and are also subject to the effect of frequency selectivefading. Hence, a receiving apparatus carries out the channel estimationdynamically. In order for the receiving apparatus to carry out thechannel estimation, two kinds of known signals are provided within aburst signal. One is the known signal, provided for all carries in thebeginning of the burst signal, which is the so-called preamble ortraining signal. The other one is the known signal, provided for part ofcarriers in the data area of the burst signal, which is the so-calledpilot signal (See Reference (1) in the following Related Art List, forinstance).

RELATED ART LIST

-   (1) Sinem Coleri, Mustafa Ergen, Anuj Puri and Ahmad Bahai, “Channel    Estimation Techniques Based on Pilot Arrangement in OFDM Systems”,    IEEE Transactions on broadcasting, vol. 48, No. 3, pp. 223-229,    September 2002.

In wireless communications, adaptive array antenna technology is one ofthe technologies to realize the effective utilization of frequencyresources. In adaptive array antenna technology, the amplitude and phaseof signals transmitted from and received by a plurality of antennas,respectively, are so controlled as to form a directional pattern of theantenna. One of techniques to realize higher data transmission rates byusing such an adaptive array antenna technology is the MIMO(Multiple-Input Multiple-Output) system. In this MIMO system, atransmitting apparatus and a receiving apparatus are each equipped witha plurality of antennas, and a channel corresponding to each of theplurality of antennas is set. That is, channels up to the maximum numberof antennas are set for the communications between the transmittingapparatus and the receiving apparatus so as to improve the datatransmission rates. Moreover, combining this MIMO system with atechnique such as the OFDM modulation scheme by which to transmitmulticarrier signals results in a higher data transmission rate.

Suppose that a system which is both not the MIMO system and one thatuses the OFDM modulation scheme (hereinafter referred to as “targetsystem”) and a system which is both the MIMO system and one that usesthe OFDM modulation scheme (hereinafter simply referred to as “MIMOsystem”) coexist in the same frequency band. In this case, if thereceiving apparatus can detect the burst signals from both the “targetsystem” and “MIMO system”, necessary signals can be reliably extractedfrom such signals. In order to facilitate the detection of such burstsignals it would be an effective way to define a common preamble signaland then place such a preamble signal in the header portion of a burstsignal. On the other hand, the receiving apparatus in the target systemcompatible with the standard such as IEEE802.11a generally demodulatesthe entire burst signals and operates to discard the burst signal if thedemodulated burst signal is false. Hence the receiving apparatus in thetarget system demodulates also the burst signal for the MIMO system. Asa result, when the traffic of burst signals in the MIMO system becomesheavy, the power consumed by the receiving apparatus increases eventhough the receiving apparatus does not demodulate the effective burstsignals.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoingcircumstances and an object thereof is to provide a receiving method andapparatus by which to suppress the increase in power consumption even ifa burst signal in a communication system which is not compatible withthe receiving apparatus arrives, and to provide also a communicationsystem utilizing said receiving method and apparatus.

In order to solve the above problems, a receiving apparatus according toa preferred embodiment comprises: a first receiver that receives a knownsignal which is in a first communication system to be communicated by apredetermined channel and which is assigned in a channel; a judgmentunit that determines whether a control signal, having a form compatiblewith the first communication system, which is in a second communicationsystem to be communicated by a plurality of channels into which achannel corresponding to the first communication system is spatiallydivided is assigned posterior to the known signal or not; a secondreceiver that receives a data signal which is assigned posterior to theknown signal and which is assigned in a channel corresponding to thefirst communication system if the judgment unit has determined that thecontrol signal is not assigned; and an instruction unit which stops anoperation of the second receiver for a data signal which is assignedposterior to the control signal and which is assigned in a plurality ofchannels, respectively, corresponding to the second communication systemif the judgment unit has determined that the control signal is assigned.

The “form compatible with the first communication system” includes aformat defined by the same number of channels as that in the firstcommunication system and a format which is defined by the differentnumber of channels as that in the first communication system but definedby a sequence of signals receivable by the first communication system.That is, preferred is the form receivable by a receiving apparatus inthe first communication system.

According to this embodiment, the control signal in the secondcommunication system has a format compatible with the firstcommunication system. Thus, the receiving apparatus can detect thecontrol signal in the second communication system. If the control signalis detected, the receiving operation will be stopped, thus suppressingthe increase in power consumption.

A data signal assigned in a channel corresponding to the firstcommunication system and the control signal may be defined in a mannersuch that constellations of signal points thereof differ from eachother. If the constellation of signal points in a position posterior tothe known signal corresponds to the constellation of signal points inthe control signal, the judgment unit may determine that the controlsignal is assigned. In this case, the presence or absence of theconstellation of a control signal can be determined.

The data signal and the control signal assigned in a channelcorresponding to the first communication system may be so defined as touse a plurality of carriers; of a plurality of carriers used for thedata signal and a plurality of carriers used for the control signal,pilot signals may be allotted to mutually corresponding carriersthereof; signal points in the pilot signals in the data signal andsignal points in the pilot signals in the control signal may be sodefined as to have the same signal point constellation and havedifferent phases; and if a phase of signal points in the pilot signalspositioned posterior to the known signal corresponds to a phase ofsignal points in the pilot signals in the control signal, the judgmentunit may determine that the control signal is assigned.

“Mutually corresponding carriers” correspond to the same carries amongthe plurality of carriers and these correspond to carriers of the samefrequency. Even if they are not the carriers that correspond to the samefrequency, it suffices if the correspondence between them is recognized.In this case, the presence or absence of the control signal can bedetermined by the difference in phase among the pilot signals

The data signal and the control signal assigned in a channelcorresponding to the first communication system may be so defined as touse a plurality of carriers; of a plurality of carriers used for thedata signal and a plurality of carriers used for the control signal,pilot signals may be allotted to mutually corresponding carriersthereof, and signal points in carriers other than pilot signals in thedata signal and signal points in carriers other than pilot signals inthe control signal may be so defined as to have different signal pointconstellations; and if signal point constellation in carriers other thanpilot signals positioned posterior to the known signal corresponds tosignal point constellation in carriers other than pilot signals in thecontrol signal, the judgment unit may determine that the control signalis assigned. In this case, the presence or absence of the control signalcan be determined by the difference in signal point constellation amongthe carriers other than the pilot signals.

The data signal assigned in a channel corresponding to the firstcommunication system and the control signal may be so defined as to usea plurality of carriers; of a plurality of carriers used for the datasignal and a plurality of carriers used for the control signal, pilotsignals may be allotted to mutually corresponding carriers thereof, andsignal points in pilot signals in the data signal and signal points inpilot signals in the control signal may be so defined as to have thesame signal point constellation and have different phases, and signalpoints in carriers other than pilot signals in the data signal andsignal points in carriers other than pilot signals in the control signalmay be so defined as to have different signal point constellations; andif a phase of signal points in pilot signals positioned posterior to theknown signal corresponds to a phase of signal points in pilot signals inthe control signal and if signal point constellation in carriers otherthan pilot signals positioned posterior to the known signal correspondsto signal point constellation in carriers other than pilot signals inthe control signal, the judgment unit may determine that the controlsignal is assigned. In this case, the presence or absence of the controlsignal can be determined by the use of difference in phase among thepilot signals and the difference in signal point constellation among thecarriers other than the pilot signals.

The instruction unit may extract from the control signal the lengths ofdata signals assigned respectively in a plurality of channelscorresponding to the second communication system, and stop an operationof the second receiver over a period of time corresponding to theextracted lengths of the data signals. A control signal in the firstcommunication system may be further assigned in a position prior to thecontrol signal in the second communication system, and the instructionunit may extract from the control signal in the first communicationsystem the lengths of data signals assigned respectively in a pluralityof channels corresponding to the second communication system, and thenstop an operation of the second receiver over a period of timecorresponding to the extracted lengths of the data signals. In thiscase, the operation is stopped based on the lengths of data signals, sothat a normal receiving processing can be executed to a burst signalthat arrives next.

Another preferred embodiment according to the present invention relatesalso to a receiving apparatus. This apparatus comprises: a firstreceiver which receives, from a transmitting apparatus in a firstcommunication system to be communicated by a predetermined channel, aknown signal assigned in a channel or receives, from a transmittingapparatus in a second communication system to be communicated by aplurality of channels into which a channel corresponding to the firstcommunication system is spatially divided, a known signal, having apredetermined relation with the known signal in the first communicationsystem, which is assigned respectively to the plurality of channels; aspecifying unit which specifies a relation among a plurality ofsignal-wave components contained in the known signal received by thefirst receiver; a second receiver that receives a data signal which isassigned posterior to the known signal and which is assigned in achannel corresponding to the first communication system if the specifiedrelation does not correspond to a relation in a known signal in thesecond communication system; and an instruction unit which stops anoperation of the second receiver for a data signal which is assignedposterior to the known signal and which is assigned in the channelcorresponding to the first communication system if the specifiedrelation corresponds to the relation in a known signal in the secondcommunication system.

The “relation” means a relationship or relationships among a pluralityof signals such as a shift in timing and the like. Here, a plurality ofsignals may be defined beforehand to be another kind of signals or theidentical signals. In the latter case, due to the effect of multi-pathin a radio channel, the signal becomes a plurality of signals whenreceived.

According to this embodiment, a relationship among a plurality of knownsignals in the second communication system is so defined as to differfrom a relationship among a plurality of signal-wave componentscontained in a known signal received by the first communication system.Thus the receiving apparatus can detect a burst signal in the secondcommunication system, based on the relationship among a plurality ofsignal-wave components contained in the received signal. If the burstsignal is detected, the receiving operation is stopped, thus suppressingthe increase in power consumption.

The specifying unit may derive, by a correlation processing between thereceived known signal and a known signal stored beforehand, a valuecorresponding to the relation among a plurality of signal-wavecomponents; if the value derived by the specifying unit is less than athreshold value corresponding to the relation in the known signal in thesecond communication system, the second receiver may determine that thespecified relation does not correspond to the relation in the knownsignal in the second communication system; and if the value derived bythe specifying unit is greater than or equal to the threshold valuecorresponding to the relation in the known signal in the secondcommunication system, the instruction unit may determine that thespecified relation corresponds to the relation in the known signal inthe second communication system. In this case, the burst signal in thesecond communication system can be detected based on the correlationprocessing.

Still another preferred embodiment according to the present inventionrelates to a receiving method. This method is characterized in that whena control signal, having a form compatible with a first communicationsystem, which is in a second communication system to be communicated bya plurality of channels into which a channel corresponding to the firstcommunication system is spatially divided is not assigned within areceived channel, a data signal assigned in the channel corresponding tothe first communication system is received, whereas when the controlsignal is assigned therein, an operation of receiving a data signalrespectively assigned in a plurality of channels corresponding to thesecond communication system is stopped.

According to this embodiment, the control signal in the secondcommunication system has a form compatible with the first communicationsystem. Thus, a control signal in the second communication system can bedetected. As a result thereof, the receiving operation is stopped whendetected, thus suppressing the increase in power consumed.

Still another preferred embodiment according to the present inventionrelates also to a receiving method. This method comprises: receiving,from a transmitting apparatus in a first communication system to becommunicated by a predetermined channel, a known signal assigned in achannel or receiving, from a transmitting apparatus in a secondcommunication system to be communicated by a plurality of channels intowhich a channel corresponding to the first communication system isspatially divided, a known signal, having a predetermined relation withthe known signal in the first communication system, which is assignedrespectively to the plurality of channels; receiving a data signal whichis assigned posterior to the known signal and which is assigned in achannel corresponding to the first communication system if a relationamong a plurality of signal-wave components contained in the receivedknown signal does not correspond to a relation in a known signal in thesecond communication system; and stopping a receiving operation for adata signal which is assigned posterior to the known signal and which isassigned respectively in the plurality of channels corresponding to thesecond communication system if the relation among a plurality ofsignal-wave components contained in the received known signalcorresponds to the relation in a known signal in the secondcommunication system.

According to this embodiment, the relationship among a plurality ofknown signals in the second communication system is so defined as todiffer from the relationship among a plurality of signal-wave componentscontained in a known signal received by the first communication system.Thus a burst signal in the second communication system can be detectedbased on the relationship among a plurality of signal-wave componentscontained in the received signal. As a result, if the burst signal isdetected, the receiving operation is stopped, thus suppressing theincrease in power consumed.

Still another preferred embodiment according to the present inventionrelates also to a receiving method. This method comprises: receiving aknown signal which is in a first communication system to be communicatedby a predetermined channel and which is assigned in a channel;determining whether a control signal, having a form compatible with thefirst communication system, which is in a second communication system tobe communicated by a plurality of channels into which a channelcorresponding to the first communication system is spatially divided isassigned posterior to the known signal or not; receiving a data signalwhich is assigned posterior to the known signal and which is assigned ina channel corresponding to the first communication system if it has beendetermined in the determining that the control signal is not assigned;and stopping an operation of the second receiver for a data signal whichis assigned posterior to the control signal and which is assigned in aplurality of channels, respectively, corresponding to the secondcommunication system if it has been determined in the determining thatthe control signal is assigned.

A data signal and the control signal assigned in a channel correspondingto the first communication system may be defined in a manner such thatconstellations of signal points thereof differ from each other. If theconstellation of signal points in a position posterior to the knownsignal corresponds to the constellation of signal points in the controlsignal, the determining may determine that the control signal isassigned. The receiving a known signal may be such that a known signalwhich is in the second communication system and which also has apredetermined relation with the known signal in the first communicationsystem and is at the same time assigned respectively in a plurality ofchannels is also received, and the determining may be such that arelation among a plurality of signal-wave components is specified andwhether the control signal is assigned or not is determined based on thespecified relation and a relation in the known signal in the secondcommunication system.

The determining may be such that a threshold value corresponding to therelation in the known signal in the second communication system isstored beforehand, a value corresponding to the relation among aplurality of signal-wave components is derived by carrying outprocessing of correlation between a received known signal and a knownsignal stored beforehand, and it is determined that the control signalis assigned if the derived value is greater than or equal to thethreshold value. The stopping may be such that the lengths of datasignals assigned respectively in a plurality of channels correspondingto the second communication system are extracted from the control signaland an operation of the receiving a data signal over a period of timecorresponding to the extracted lengths of the data signals. A controlsignal in the first communication system may be further assigned in aposition prior to the control signal in the second communication system,and the stopping may be such that the lengths of data signals assignedrespectively in a plurality of channels corresponding to the secondcommunication system are extracted from the control signal in the firstcommunication system and then an operation of the receiving a datasignal is stopped over a period of time corresponding to the extractedlengths of the data signals.

The data signal and the control signal assigned in a channelcorresponding to the first communication system may be so defined as touse a plurality of carriers; of a plurality of carriers used for thedata signal and a plurality of carriers used for the control signal,pilot signals may be allotted to mutually corresponding carriersthereof; signal points in the pilot signals in the data signal andsignal points in the pilot signals in the control signal may be sodefined as to have the same signal point constellation and havedifferent phases; and if a phase of signal points in the pilot signalspositioned posterior to the known signal corresponds to a phase ofsignal points in the pilot signals in the control signal, thedetermining may determine that the control signal is assigned.

The data signal and the control signal assigned in a channelcorresponding to the first communication system may be so defined as touse a plurality of carriers; of a plurality of carriers used for thedata signal and a plurality of carriers used for the control signal,pilot signals may be allotted to mutually corresponding carriersthereof, and signal points in carriers other than pilot signals in thedata signal and signal points in carriers other than pilot signals inthe control signal may be so defined as to have different signal pointconstellations; and if signal point constellation in carriers other thanpilot signals positioned posterior to the known signal corresponds tosignal point constellation in carriers other than pilot signals in thecontrol signal, the determining may determine that the control signal isassigned.

The data signal and the control signal assigned in a channelcorresponding to the first communication system may be so defined as touse a plurality of carriers; of a plurality of carriers used for thedata signal and a plurality of carriers used for the control signal,pilot signals may be allotted to mutually corresponding carriersthereof, and signal points in pilot signals in the data signal andsignal points in pilot signals in the control signal may be so definedas to have the same signal point constellation and have differentphases, and signal points in carriers other than pilot signals in thedata signal and signal points in carriers other than pilot signals inthe control signal may be so defined as to have different signal pointconstellations; and if a phase of signal points in pilot signalspositioned posterior to the known signal corresponds to a phase ofsignal points in pilot signals in the control signal and if signal pointconstellation in carriers other than pilot signals positioned posteriorto the known signal corresponds to signal point constellation incarriers other than pilot signals in the control signal, the determiningmay determine that the control signal is assigned.

Still another preferred embodiment according to the present inventionrelates also to a receiving method. This method comprises: receiving,from a transmitting apparatus in a first communication system to becommunicated by a predetermined channel, a known signal assigned in achannel or receiving, from a transmitting apparatus in a secondcommunication system to be communicated by a plurality of channels intowhich a channel corresponding to the first communication system isspatially divided, a known signal, having a predetermined relation withthe known signal in the first communication system, which is assignedrespectively to the plurality of channels; specifying a relation among aplurality of signal-wave components contained in the known signalreceived by the first receiver; receiving a data signal which isassigned posterior to the known signal and which is assigned in achannel corresponding to the first communication system if the specifiedrelation does not correspond to a relation in a known signal in thesecond communication system; and stopping an operation of the secondreceiver for a data signal which is assigned posterior to the knownsignal and which is assigned in the channel corresponding to the firstcommunication system if the specified relation corresponds to therelation in a known signal in the second communication system.

The specifying may be such that a value corresponding to the relationamong a plurality of signal-wave components is derived by a correlationprocessing between the received known signal and a known signal storedbeforehand; if the value derived by the specifying unit is less than athreshold value corresponding to the relation in the known signal in thesecond communication system, the receiving a data signal may determinethat the specified relation does not correspond to the relation in theknown signal in the second communication system; and if the valuederived by the specifying unit is greater than or equal to the thresholdvalue corresponding to the relation in the known signal in the secondcommunication system, the stopping may determine that the specifiedrelation corresponds to the relation in the known signal in the secondcommunication system.

Still another preferred embodiment according to the present inventionrelates to a communication system. This system comprises: a firsttransmitting apparatus that transmits a known signal, corresponding to afirst communication system to be communicated by a predeterminedchannel, which is assigned in a channel and a data signal which isassigned posterior to the known signal; a second transmitting apparatusthat transmits a known signal and control signal having each formscompatible with the first communication system and a secondcommunication system to be communicated by a plurality of channels intowhich a channel corresponding to the first communication system isspatially divided, and transmits also a data signal assigned,respectively in the plurality of channels, in a position posterior tothe known signal and control signal; and a receiving apparatus,corresponding to the first communication system, which receives the datasignal assigned posterior to the known signal if the control signal doesnot exist in a position posterior to the known signal, and stopsreceiving for the data signal assigned respectively in the plurality ofchannels if the control signal exits in a position posterior to theknown signal.

According to this embodiment, the control signal in the secondcommunication system has a form compatible with the first communicationsystem, so that the control signal in the second communication systemcan be detected. As a result, the receiving operation can be stoppedwhen detected, thus suppressing the increase in power consumption.

It is to be noted that any arbitrary combination of the above-describedstructural components and expressions changed among a method, anapparatus, a system, a recording medium, a computer program and so forthare all effective as and encompassed by the present embodiments.

Moreover, this summary of the invention does not necessarily describeall necessary features so that the invention may also be sub-combinationof these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described by way of examples only, withreference to the accompanying drawings which are meant to be exemplary,not limiting and wherein like elements are numbered alike in severalFigures in which:

FIG. 1 illustrates a spectrum of a multicarrier signal according to afirst embodiment of the present invention.

FIG. 2 illustrates a concept of a MIMO system according to the firstembodiment.

FIG. 3 illustrates a structure of a communication system according tothe first embodiment.

FIG. 4A and FIG. 4B each show a structure of a burst format relative toFIG. 3.

FIG. 5 illustrates a structure of a MIMO transmitting apparatus shown inFIG. 3.

FIG. 6 illustrates a structure of a target receiving apparatus shown inFIG. 3.

FIGS. 7A to 7D show constellations of signals contained in the burstformats shown in FIGS. 4A and 4B.

FIG. 8 illustrates a structure of a judgment unit shown in FIG. 6.

FIG. 9 is a flowchart showing a procedure of receiving operation by atarget receiving apparatus shown in FIG. 6.

FIG. 10 illustrates a structure of a burst format according to a secondembodiment of the present invention.

FIG. 11 illustrates a structure of a target receiving apparatusaccording to the second embodiment.

FIG. 12 is a flowchart showing a procedure of receiving operation by atarget receiving apparatus shown in FIG. 11.

FIG. 13 illustrates a structure of a judgment unit according to a thirdembodiment of the present invention.

FIG. 14 is a flowchart showing a judgment procedure by a judgment unitshown in FIG. 13.

FIG. 15 illustrates a structure of another judgment unit according tothe third embodiment.

FIG. 16 illustrates a structure of still another judgment unit accordingto the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on the following embodimentswhich do not intend to limit the scope of the present invention butexemplify the invention. All of the features and the combinationsthereof described in the embodiments are not necessarily essential tothe invention.

First Embodiment

Before describing the present invention in detail, an outline of thepresent invention will be described first. A first embodiment of thepresent invention relates to a system which is both not a MIMO systemand one that uses an OFDM modulation scheme (hereinafter referred to as“target system” as described before). Here, in the same frequency bandas the target system, there coexists a system which is both a MIMOsystem and one that uses an OFDM modulation scheme (hereinafter referredto as “MIMO system” as described earlier). Here, in both the targetsystem and the MIMO system, a common preamble is assigned in a headerportion of packet signal. It is to be noted that a transmittingapparatus, equipped with a plurality of antennas, in the MIMO systemtransmits the preamble from one of the plurality of antennas but notfrom the remaining antennas.

Here, the packet signal in a target system is such that a preamble, acontrol signal and data are assigned in this order. In the presentembodiment, on the other hand, the packet signal in a MIMO system issuch that a preamble of the target system, a control signal of thetarget system, a control signal of the MIMO system, a preamble of theMIMO system and data of the MIMO system are assigned in this order.Here, the preamble of the target system, the control signal of the MIMOsystem and the control signal of the MIMO system are transmitted from asingle antenna. That is, they are in the form of a burst signal.

As a result thereof, the receiving apparatus can receive these signals.On the other hand, the preamble of the MIMO system and the data of theMIMO system are transmitted from a plurality of antennas, so that theyare not subject to and not a target for the receiving in the receivingapparatus.

A receiving apparatus in a target system according to the presentinvention receives these preambles and checks on the arrival of packetsignals. The packet signals in the target system and the MIMO system aresuch that the preamble of the target system and the control signal ofthe target system are used in common therebetween. On the other hand,the data of the target system and the control signal of the MIMO systemassigned posterior thereto are defined such that their signal pointconstellations differ. The receiving apparatus determines, from thesignal point constellation, if a signal assigned posterior to thecontrol signal of the target system is either the data of the targetsystem or the control signal of the MIMO system. In the former case, thereceiving apparatus continues the demodulation. In the latter case, thereceiving apparatus stops the demodulation. It is assumed herein that atarget system is a wireless LAN conforming to the IEEE802.11a standardand a MIMO system is a wireless LAN in which the IEEE802.11n standard isto be implemented.

FIG. 1 illustrates a spectrum of a multicarrier signal according to afirst embodiment. Since, as described above, the target system and theMIMO system use the OFDM modulation scheme, FIG. 1 shows a spectrum of asignal in the OFDM modulation scheme compatible with the target systemand the MIMO system. One of a plurality of carriers in an OFDMmodulation scheme is generally called a subcarrier. Herein, however,each of the subcarriers is designated by a “subcarrier number”. Asillustrated in FIG. 1, the IEEE802.11a standard defines 53 subcarriers,namely, subcarrier numbers “−26” to “26”. It is to be noted that thesubcarrier number “0” is set to null so as to reduce the effect of adirect current component in a baseband signal. The respectivesubcarriers are modulated by BPSK (Binary Phase Shift Keying), QPSK(Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation)and 64QAM.

FIG. 2 illustrates a concept of a MIMO system according to the firstembodiment. The MIMO system includes a MIMO transmitting apparatus 10and a MIMO receiving apparatus 12. The MIMO transmitting apparatus 10includes a first transmitting antenna 14 a and a second transmittingantenna 14 b, which are generically called transmitting antennas 14, andthe MIMO receiving apparatus 12 includes a first receiving antenna 16 aand a second receiving antenna 16 b, which are generically calledreceiving antennas 16. Though the MIMO receiving apparatus 12 is notdirectly relevant to the present embodiment, the MIMO system will bedescribed while the MIMO receiving apparatus 12 is discussed herein asappropriate.

The MIMO transmitting apparatus 10 transmits predetermined signals andtransmits different signals from the first transmitting antenna 14 a andthe second transmitting antenna 14 b. The MIMO receiving apparatus 12receives the signals transmitted from the first transmitting antenna 14a and the second transmitting antenna 14 b by the first receivingantenna 16 a and the second receiving antenna 16 b. The MIMO receivingapparatus 12 separates received signals by adaptive array signalprocessing and demodulates the signals transmitted from the firsttransmitting antenna 14 a and the second transmitting antenna 14 bindependently.

Here, if channel characteristic between the first transmitting antenna14 a and the first receiving antenna 16 a is denoted by h₁₁, thatbetween the first transmitting antenna 14 a and the second receivingantenna 16 b by h₁₂, that between the second transmitting antenna 14 band the first receiving antenna 16 a by h₂₁, and that between the secondtransmitting antenna 14 b and the second receiving antenna 16 b by h₂₂,then the MIMO receiving apparatus 12 operates in such a manner as toactivate h₁₁ and h₂₂ only by an adaptive array signal processing anddemodulate the signals transmitted from the first transmitting antenna14 a and the second transmitting antenna 14 b independently.

FIG. 3 shows a structure of a communication system 100 according to thefirst embodiment. The communication system 100 includes a MIMOtransmitting apparatus 10, a target transmitting apparatus 50 and atarget receiving apparatus 54. The target transmitting apparatus 50includes an antenna 52, and the target receiving apparatus 54 includes areceiving antenna 56. Here, the target transmitting apparatus 50 and thetarget receiving apparatus 54 correspond to a target system, whereas theMIMO transmitting apparatus 10 corresponds to a MIMO system.

The target transmitting apparatus 50 transmits signals from thetransmitting antenna 52. Thus, the target transmitting apparatus 50 setsone channel, corresponding to the target system, for the transmittingantenna 52. That is, the target transmitting apparatus 50 transmits, inthe format of burst signals, a preamble assigned in the channel and dataassigned posterior to the preamble. Here, “one channel” means the numberof channels set at a predetermined instant.

As described above, the MIMO transmitting apparatus 10 transmit signalsindependently from the first transmitting antenna 14 a and the secondtransmitting antenna 14 b, respectively. Hence, the MIMO transmittingapparatus 10 sets two channels for the first transmitting antenna 14 aand the second transmitting antenna 14 b, respectively. The two channelsare set by spatially dividing a channel corresponding to the targetsystem. A preamble and a control signal having the format of the targetsystem are added to a header portion of a channel so that the targetreceiving apparatus 54 can receive said channel. As a result, the MIMOtransmitting apparatus 10 transmits, in a burst signal format, thepreamble and control signal having a channel format compatible with thetarget system and data, positioned posterior thereto, which are assignedto a plurality of channels, respectively. It is assumed herein that thecontrol signal is a signal compatible with the MIMO system.

The target receiving apparatus 54, which corresponds to the targetsystem, receives signals received from the MIMO transmitting apparatus10, namely, two signals sent independently from the first transmittingantenna 14 a and the second transmitting antenna 14 b or receivessignals sent from the target transmitting apparatus 50. Now, if amongthe received burst signals a control signal corresponding to the MIMOsystem does not exist in a position posterior to the preamble, thetarget receiving apparatus 54 judges that the received burst signals areburst signals in the target system. As a result of this, a receivingprocessing is performed on data assigned in the received burst signals.On the other hand, if among the received burst signals a control signalcorresponding to the MIMO system exists in a position posterior to thepreamble, the target receiving apparatus 54 judges that the receivedburst signals are those in the MIMO system. As a result of this, thetarget receiving apparatus 54 stops the receiving processing for thedata of the MIMO system that follows the control signal corresponding tothe MIMO system.

FIG. 4A and FIG. 4B each show a structure of a burst format. FIG. 4Ashows the burst format of a target system and corresponds to that of atraffic channel of IEEE802.11a standard. “Target STS (Short TrainingSequence)” and “Target LTS (Long Training Sequence)” shown in FIG. 4Aand FIG. 4B correspond to a preamble. These are the “STS” and “LTS”defined in the IEEE802.11a standard but are shown as such in FIG. 4A andFIG. 4B to indicate that these are compatible the target system.

“Target signal” is a signal for a target system and corresponds to acontrol signal. “Target data” is data for the target system. The “targetSTS”, “target LTS”, “target signal”, and “target data” are respectivelycompatible with the OFDM modulation scheme. In the IEEE802.11a standard,the size of Fourier transform is 64 (hereinafter the points of one FFT(Fast Fourier Transform) will be called “FFT point”) and the FFT pointnumber of a guard interval is 16. In the OFDM modulation scheme, thetotal sum of the size of Fourier transform and the FFT point number of aguard interval generally constitutes one unit. This “one unit” is calledan OFDM symbol in the present embodiments. Hence, the OFDM symbolcorresponds to 80 FFT points.

Here, the “target LTS” and “target signal” have each the length of “2OFDM symbols” and the “data” has arbitrary length. The total length of“target STS” is “2 OFDM symbols”. However, the signal of “16 FFT points”is repeated ten times, so that the structure thereof differs from thatof the “target LTS” and the like. The preambles such as “target STS” and“target LTS” are known signals transmitted to execute the setting ofAGC, timing synchronization and carrier recovery and the like in thetarget receiving apparatus 54. The burst signals such as the abovecorrespond to one channel in the target system.

FIG. 4B shows a burst format of a MIMO system. It is assumed herein thatthe number of antennas used for transmission in the MIMO system is “2”,and this corresponds to the first transmitting antenna 14 a and thesecond transmitting antenna 14 b of FIG. 3. In FIG. 4B, the upper rowcorresponds to a burst signal transmitted from the first transmittingantenna 14 a whereas the lower row corresponds to a burst signaltransmitted from the second transmitting antenna 14 b. In the burstsignal in the upper row of FIG. 4B, “target STS”, “target LTS” and“target signal” are assigned in this order starting from the top. Thisarrangement is the same as the above case of the target system. “MIMOsignal”, which is a control signal in the MIMO system, is assignedposterior to the “target LTS”. The “MIMO signal” has a channel formatcompatible with the target system, namely, the format of a channel thatuses an antenna for transmission.

For the first transmitting antenna 14 a, “first MIMO-STS”, “firstMIMO-LTS” and “first MIMO-data” are assigned posterior to the “MIMO”signal, as STS, LTS and data compatible with the MIMO system,respectively. On the other hand, for the second transmitting antenna 14b, “second MIMO-STS”, “second MIMO-LTS” and “second MIMO-data” areplaced as STS, LTS and data compatible with the MIMO system,respectively.

The above-described burst signals correspond to two spatially dividedchannels in the MIMO system. Signals included in the “first MIMO-STS”and the like are defined by a predetermined signal pattern. Though inFIG. 4B the burst signals, which correspond to the two transmittingantennas 14 a and 14 b and correspond therefore to the two channels,have been described above, they are not limited to the two channels andmore than two channels may be set.

FIG. 5 illustrates a structure of a MIMO transmitting apparatus 10. TheMIMO transmitting apparatus 10 includes a data separating unit 20, afirst modulation unit 22 a, a second modulation unit 22 b, . . . and anNth modulation unit 22 n, which are generically referred to asmodulation units 22, a first radio unit 24 a, a second radio unit 24 b,. . . and an Nth radio unit 24 n, which are generically referred to asradio units 24, a control unit 26, and a first transmitting antenna 14a, a second transmitting antenna 14 b, . . . and an Nth transmittingantenna 14 n, which are generically referred to as transmitting antennas14. The first modulation unit 22 a includes an error correcting unit 28,an interleave unit 30, a preamble adding unit 32, an IFFT unit 34, a GIunit 36 and a quadrature modulation unit 38. The first radio unit 24 aincludes a frequency conversion unit 40 and an amplification unit 42.

The data separating unit 20 separates data to be transmitted into thenumber of data equal to that of antennas. The error correcting unit 28performs a coding for error correction on data. The coding to beemployed here is a convolutional coding, and the coding rate is to beselected from prescribed values. The interleave unit 30 interleaves dataafter the convolutional coding. The preamble adding unit 32 adds a“target STS” and a “target LTS” to a header portion of a burst signal.The preamble adding unit 32 further adds a “first MIMO-STS” and a “firstMIMO-LTS”. Thus, it is assumed herein that the preamble adding unit 32stores the “target STS”, “first MIMO-STS” and the like.

The IFFT unit 34 performs IFFT (Inverse Fast Fourier Transform) in unitsof FFT point, thereby converting a frequency-domain signal using aplurality of subcarriers into a signal in time domain. The GI unit 36adds a guard interval to time-domain data. The quadrature modulationunit 38 carries out quadrature modulation. The frequency conversion unit40 performs a frequency conversion transforming a quadrature-modulatedsignal into a radio frequency signal. The amplification unit 42 is apower amplifier for amplifying radio frequency signals. Finally, signalshaving a format as shown in FIG. 4B are transmitted from a plurality oftransmitting antennas 14. The control unit 26 controls the timing andother functions of the MIMO transmitting apparatus 10. It is to be notedthat in the present embodiment the transmitting antennas 14 arenon-directional and the MIMO transmitting apparatus 10 does not performadaptive array signal processing. In the above-described structure, theerror correcting unit 28 and the interleave unit 30 may be provided in aposition anterior to the data separating unit 20. If they are positionedanterior to the data separating unit 20, the signals coded by the errorcorrecting unit 28 and then interleaved by the interleave unit 30 areseparated by the data separating unit 20. It is assumed herein that thetarget transmitting apparatus 50 shown in FIG. 3 is provided with thefirst modulation unit 22 a and the first radio unit 24 a.

FIG. 6 illustrates a structure of a target receiving apparatus 54. Thetarget receiving apparatus 54 includes a radio unit 60, a basebandprocessing unit 62, a control unit 64 and an instruction unit 74. Thebaseband processing unit 62 includes a quadrature detection unit 66, anFFT unit 68, a demodulation unit 70 and a judgment unit 72.

The radio unit 60 carries out frequency conversion processing ofreceived radio frequency signal into received baseband signals, and theradio unit 60 also carries out amplification processing, A-D conversionprocessing and the like. Since the communication system 100 assumedherein employs a wireless LAN conforming to the IEEE802.11a standard,the radio frequency is in the 5 GHz band. Here, the target transmittingapparatus 50 receives burst signals in the target system or burstsignals in the MIMO system. In either case, however, it receives targetSTSs and target LTSs assigned in a channel.

The quadrature detection unit 66 performs a quadrature detection of thereceived signals which has been converted to the baseband by the radiounit 60. The quadrature-detected signal, which contains in-phasecomponents and quadrature components, is generally represented by twosignal lines. For the clarity of explanation, the signal is presentedhere by a single signal line, and the same will be applied hereinafter.The FFT unit 68 performs FFT on the received signals which have beenquadrature-detected by the quadrature detection unit 66, and convertsthem from time-domain signals to frequency-domain signals. The FFT unit68 also removes guard intervals. The demodulator 70 estimates a radiochannel for both the burst signals in the target system and the burstsignals in the MIMO system, based on the target LTS, and thendemodulates the target signal and the like placed posterior to thetarget LTS, based on the estimated radio channel. The demodulator 70also carries out the deinterleave and decoding processing. It is to benoted that although the target STS is used to set AGC (not shown) andexecute the timing synchronization, any conventional technique may beused for these and therefore the explanation therefor is omitted here.

The judgment unit 72 determines if the MIMO signal having a form of achannel corresponding to the target system is assigned in a positionposterior to the target LTS and the target signal. The difference insignal point constellation between a target data and a MIMO signal isused to make the above decision. That is, the target data assigned in achannel corresponding to the target system and the MIMO signal aredefined beforehand in a manner such that the constellations of signalpoints thereof differ from each other.

FIGS. 7A to 7D show the constellations of signals contained in burstformats shown in FIGS. 4A and 4B. FIG. 7A shows a constellation for aMIMO signal. Referring to FIG. 7A, the modulation scheme of the MIMOsignal is compatible with BPSK, and the signal points thereof aredefined such that the quadrature components are placed at either “+1” or“−1”. That is, the constellation is defined such that the in-phasecomponent lies at “0”. FIG. 7B shows a constellation for target data.Referring to FIG. 7B, the modulation scheme of the target data is alsocompatible with BPSK. The signal points of the target data are definedsuch that the in-phase components are placed at either “+1” or “−1” andthe quadrature component lies at “0”.

As a result, the MIMO signal and the target signal are such that theirrespective values of in-phase components and quadrature components forsignal points differ. The MIMO signal can be discriminated from thetarget data and vice versa by detecting this difference. The modulationschemes are switched around, as appropriate, for the target data andQPSK, 16QAM or 64QAM may be used in addition to BPSK. FIG. 7C shows aconstellation of target data when the modulation scheme is QPSK. FIG. 7Dshows a constellation of target data when the modulation scheme is16QAM. Similar to the case when the modulation scheme is BPSK, thetarget data can be discriminated from the MIMO signal and vice versabased on the values of in-phase components and quadrature components forthe signal points.

Let us now go back to FIG. 6. As described above, if the constellationof a signal point in the position posterior to the target LTS and targetsignal corresponds to the constellation of a signal point in the MIMOsignal, it is judged by the judgment unit 72 that a MIMO signal isassigned in the received burst signal. If it is judged by the judgmentunit 72 that the MIMO signal is not assigned, the demodulation unit 70continues to carry out demodulation, so that the demodulation unit 70demodulates a target data signal assigned in a position posterior to thetarget LTS and target signal. That is, in this case, the targetreceiving apparatus 54 determines that the burst signal corresponding tothe target system has been received and then the target receivingapparatus 54 receives in a usual manner the burst signal correspondingto the target system.

When it is judged by the judgment unit 72 that the MIMO signal has beenassigned, the instruction unit 74 stops the operation of the basebandprocessing unit 62 for MIMO-STS, MIMO-LTS, MIMO-data and the like whichare assigned in positions posterior to the MIMO signal. That is, in thiscase, the target receiving apparatus 54 determines that the burst signalcorresponding to the MIMO system has been received and then stopsreceiving processing for the burst signal corresponding to the MIMOsystem. In so doing, the instruction unit 74 extracts the length of thefirst MIMO-data or the like assigned respectively in a plurality ofchannels corresponding to the MIMO system, and stops the operation ofthe baseband processing unit 62 over a period of time corresponding tothe extracted length of the first MIMO-data or the like. The controlunit 64 controls the timing and the like of the target receivingapparatus 54.

In terms of hardware, this structure can be realized by a CPU, a memoryand other LSIs of an arbitrary computer. In terms of software, it isrealized by memory-loaded programs or the like, but drawn and describedherein are function blocks that are realized in cooperation with those.Thus, it is understood by those skilled in the art that these functionblocks can be realized in a variety of forms such as by hardware only,software only or the combination thereof.

FIG. 8 illustrates a structure of a judgment unit 72. The judgment unitincludes an I-component processing unit 80, a Q-component processingunit 82, a decision unit 84 and a condition storage 86.

The I-component processing unit 80 specifies the amplitude of anin-phase component of the demodulated signal. In so doing, theI-component processing unit 80 may carry out a statistical processingsuch as averaging. On the other hand, the Q-component processing unit 82specifies the amplitude of a quadrature component of the demodulatedsignal. In so doing, the Q-component processing unit 82 may carry outthe statistical processing such as averaging.

The condition storage 86 stores conditions for signal points to decideon a case when the signal points correspond to a MIMO signal. As shownin FIG. 7A, the signal points corresponding to the MIMO signal do nothave the in-phase component at a transmitting side. Thus, a case wherethe absolute value of an in-phase component is smaller than apredetermined threshold value is defined, in the condition storage 86,to be the case corresponding to the MIMO signal. Here, the thresholdvalue is defined to be a value where the noise is taken into account,and is set in such a manner as to be smaller than the absolute value ofthe signal point “+1” or “−1” of an in-phase component as in FIG. 7B.The condition storage 86 may employ the definition where the quadraturecomponent is also used. A case where a result obtained by dividing anin-phase component value by a quadrature component value is smaller thana predetermined threshold value may be defined to be the casecorresponding to the MIMO signal.

The decision unit 84 receives, from the I-component processing unit 80and the Q-component processing unit 82, the inputs of an in-phasecomponent value and a quadrature component value of the demodulatedsignal, respectively. Then, based on the conditions inputted from thecondition storage 86 the decision unit 84 determines if the inputtedsignal is signal points corresponding to the MIMO signal. The decisionunit 84 may make decision from a pair of in-phase component value andquadrature component value for the demodulated signal, or from in-phasecomponent values and quadrature component values for the signals of aplurality of subcarriers that correspond to a single symbol. If thesignal points of a received signal is determined to be those thatcorrespond to the MIMO signal, the judgment unit 72 will output theresult of decision to the instruction unit 74.

An operation of the target receiving apparatus 54 structured as abovewill now be described. FIG. 9 is a flowchart showing a procedure ofreceiving operation by a target receiving apparatus 54. When the targetreceiving apparatus 54 receives a target STS and a target LTS (Y ofS10), the judgment unit 72 checks on the constellation of signal pointsplaced posterior to the target signal (S12). If the signal pointconstellation corresponds to the constellation of signal points in theMIMO signal (Y of S14), the instruction unit 74 will acquire the datalength from the MIMO signal (S16). Then a stoppage period is determinedfrom the acquired data length (S18), and the instruction unit 74 stopsthe operation of the baseband processing unit 62 (S20). If, on the otherhand, the signal point constellation does not correspond to theconstellation of signal points in the MIMO signal (N of S14), thedemodulation unit 70 demodulates the target data (S22). If the targetreceiving apparatus 54 does not receive the target STS and target LTS (Nof S10), the processing is terminated.

According to the first embodiment, the MIMO signal in a MIMO system hasa form of a channel corresponding to a target system, so that the targetreceiving apparatus can detect the MIMO signal. When the MIMO signal isdetected, the receiving operation is stopped, so that the increase inpower consumption can be suppressed. Furthermore, the MIMO signal is notassigned in a far-back position of a burst signal but assigned in aposition halfway or well within the burst signal. Thus, even when theburst signal has not yet been received fully to cover the entire portionthereof, the target receiving apparatus can determine a communicationsystem associated with the burst signal. Furthermore, the targetreceiving apparatus can receive the burst signal corresponding to atarget system without ever receiving the burst signal corresponding tothe MIMO system. Since the burst signal corresponding to the MIMO systemis not received, the effect of the MIMO system can be minimized.

Since the increase in power consumption can be suppressed, the increasein size of battery can be prevented even if the target receivingapparatus is driven by the battery or the like. Since the increase inpower consumption can be suppressed, the battery driving time can beextended even if the target receiving apparatus is powered by thebattery. The target receiving apparatus can be made smaller in size. Thepresence or absence of the constellation of a MIMO signal can bedetermined by a difference in signal point constellation. Since thedifference in the signal point constellation is utilized, the decisioncan be made at an earlier stage. Since the period during which theoperation is stopped can be adjusted based on the length of MIMO-data inthe MIMO system, a normal receiving processing can be performed on aburst signal arriving next.

Second Embodiment

Similar to the first embodiment, a second embodiment according to thepresent invention relates to a receiving apparatus which receives burstsignals from a transmitting apparatus corresponding to a target systemand a transmitting apparatus corresponding to a MIMO system, continuesthe receiving of the burst signals if the burst signal corresponds tothe target system and stops the receiving of the burst signals if theburst signal corresponds to the MIMO system. However, the secondembodiment differs from the first embodiment in the following twopoints.

The first point that differs from the first embodiment is as follows.The format of burst singles for the MIMO system differs, and the “targetSTSs” and the like are transmitted also from antennas, which do nottransmit the “target STSs”, during a period in which the “target STSs”and the like are transmitted. However, the “target STS” is nottransmitted intact but it is transmitted while the timing of the signalis being shifted cyclically within the “target STS”. For example, when asignal for a predetermined FFT point is shifted behind by two points,the signal assigned for the endmost two points is assigned in thebeginning.

The second point is that a method, for determining if the received burstsignal corresponds to the target system or MIMO system, differs in thereceiving apparatus. The receiving apparatus stores beforehand thesignal patterns of target STS or target LTS, and carries out processingof correlation between the signal pattern and the received burst signal.If the received burst signal corresponds to the target system, intervalsamong a plurality of peaks as a result of the correlation processingcorrespond to time difference among incoming waves in a radio channel.If, on the other hand, the burst signal corresponds to a MIMO system,the intervals among a plurality of peaks as a result of the correlationprocessing correspond to the difference in timing of the signals whichhave been shifted beforehand. If the difference in timing of the signalsis defined to be greater than the time difference among a plurality ofincoming waves in the radio channel, whether the received burst signalcorresponds to a target system or MIMO system can be determined from theresult of correlation processing.

FIG. 10 illustrates a structure of a burst format according to a secondembodiment of the present invention. FIG. 10 shows a burst format of aMIMO system. Since the burst format of a target system is the same asthat shown in FIG. 4A, the repeated explanation thereof is omitted.Similar to FIG. 4B, the number of antennas used for transmission in theMIMO system is “2” in FIG. 10. A burst signal transmitted from the firsttransmitting antenna 14 a is shown in the upper row of FIG. 10. A burstsignal transmitted from the second transmitting antenna 14 b is shown inthe lower row of FIG. 10. Since the burst signal shown in the upper rowof FIG. 10 is the same as the burst signal shown in the upper row ofFIG. 4B, the description thereof is omitted. Of the burst signal shownin the lower row of FIG. 10, “second MIMO-STS”, “second MIMO-LTS” and“second MIMO-data” are the same as those shown in the lower row of FIG.4B.

“Target STS+CDD”, “target LTS+CDD”, “target signal+CDD” and “MIMOsignal+CDD” are so assigned in the burst signal transmitted from thesecond transmitting antenna 14 b as to respectively correspond to“target STS”, “target LTS”, “target signal” and “MIMO signal”transmitted from the first transmitting antenna 14 a. Here, “targetSTS+CDD” is equivalent to a case where the pattern of signal containedtherewithin is the same as the pattern of signals contained in the“target STS” but the positions of the signals assigned differ. Here, the“target STS” is constituted by 160 FFT points.

For example, the signal at the FFT point of the beginning of “targetSTS” is in such a relation as to be assigned at the eighth FFT point of“target STS+CDD”. Furthermore, the signals at the endmost eight FFTpoints of “target STS+CDD” are in such a relation as to be assigned tothe eight FFT points from the beginning of “target STS+CDD”. In thismanner, the signals are so assigned that the timings of signals areshifted. The relationship in which the timing is shifted in such a caseas in “target STS” and “target STS+CDD” will be hereinafter simplyreferred to as “relation”.

In the IEEE801.11a standard, an interval between FFT points is definedto be 50 ns. Here, a shift amount of signal timing is 8 FFT points. As aresult, the timing error between “target STS” and “target STS+CDD” isdefined to be 400 ns. The same also applies to “target LTS+CDD”, “targetsignal+CDD” and “MIMO signal+CDD”. That is, “target STS+CDD” and thelike in the MIMO system has a predetermined relation with “target STS”and the like in the target system.

FIG. 11 illustrates a structure of a target receiving apparatus 54according to the second embodiment. The target receiving apparatus 54includes a receiving antenna 56, a radio unit 60, a baseband processingunit 62, a control unit 64 and an instruction unit 74. The basebandprocessing unit 62 includes a quadrature detection unit 66, an FFT unit68, a demodulation unit 70 and a detection unit 88. The detection unit88 includes a correlation processing unit 90, a pattern storage 92, apeak detector 94, a decision unit 96 and a threshold value storage 98.Of these components, the description of those executing the sameoperations as the target receiving apparatus 54 of FIG. 6 is omitted.

The radio unit 60 receives the target STSs or target LTSs assigned to achannel, from a target transmitting apparatus 50 in a target system. Theradio unit 60 further receives, from a MIMO transmitting apparatus in aMIMO system, the target STSs+CDDs and target LTSs+CDDs, having apredetermined relation with the target STS and target LTS in the targetsystem, which are assigned respectively to a plurality of channels. Thetarget transmitting apparatus 50 and the MIMO transmitting apparatus 10are those as shown in FIG. 3.

The pattern storage 92 stores the patterns of target STSs and targetLTSs which are known signals. That is, the target STSs are expressed inthe time domain and the pattern storage 92 stores the signalscorresponding to 16 FFT points among them, whereas the target LTSs areexpressed in the time domain and the pattern storage 92 stores thesignals corresponding to 64 FFT points among them. Between the targetSTSs and the target LTSs, the pattern storage may store either one ofthe signal patterns. In such a case, a processing that uses either oneof the target STS or the target LTS is carried out in the correlationprocessing unit 90, peak detector 94 and decision unit 96, respectively,which will be described later.

The correlation processing unit 90 performs correlation processing onthe burst signal, which has been subjected to quadrature detection bythe quadrature detection unit 66, and the target STS and target LTSstored in the pattern storage 92. The correlation processing unit 90 hasa structure of a matched filter, and holds, as tap coefficients of afilter, the target STSs and target LTSs stored in the pattern storage92. The correlation processing unit 90 inputs the quadrature-detectedburst signals to the matched filter. As a result of the aboveprocessing, a result of correlation processing is obtained ascorrelation values with respect to time. If the relation between theinputted burst signals and the tap coefficient values becomes closer,the correlation value will become larger. In this manner, thecorrelation processing unit 90 uses the received target STSs and/orreceived LTSs and the target STSs and/or target LTSs stored beforehandso as to derive relations among a plurality of signal componentscontained in the received target STSs and/or target LTSs as thecorrelation values.

The peak detector 94 detects at least two peaks of the correlationvalues from the result of correlation processing by the correlationprocessing unit 90. For example, the peak detector 94 detects at leasttwo peaks in the area of two OFDM symbols corresponding to a target STS.Here, if the inputted burst signal is the burst signal in the targetsystem, said burst signal uses a channel. Thus, in the result ofcorrelation processing, a peak appears at timing when a delayed wave ina radio channel exists. In a radio channel assumed in the IEEE802.11astandard, it is assumed that a delayed wave arrives after the delay ofabout some ten nanoseconds from the preceding wave. As described above,the aforementioned “relation” is also caused by the radio channel.

If, on the other hand, the inputted burst signal is a burst signal inthe MIMO signal, a plurality of burst signals assigned to a plurality ofchannels are received in a combined manner. When the target STS assignedto a burst signal is being received as in FIG. 10, the target STS+CDD isalso received. As described earlier, the target STS is in a relation tothe target STS+CDD such that the signal timing is shifted. For example,if the shift amount of the signal timing is 8 FFT points, two peaks aredetected in the positions away from about 8 FFT point apart. Since 8 FFTpoints are equivalent to 400 ns here, the effect of the delayed wave onthe aforementioned radio channel is equivalent to as small as an erroronly.

The threshold value storage 98 holds threshold values with which the atleast two peaks detected by the peak detector 94 are to be compared. Inthe above example, the threshold value is set to 300 nsec. In thismanner, the threshold values are defined based on a value correspondingto a relation in a target STS and/or target LTS in a MIMO system.

The decision unit 96 compares the thus detected at least two peaks,namely, the relation in the inputted burst signal, with a thresholdvalue, and decides if the inputted burst signal corresponds to thetarget system or MIMO system. That is, if the detected at least twopeaks are less than the threshold value, it is determined that therelation among a plurality of signal-wave components in the inputtedburst signal does not correspond to the relation in the target STSand/or target LTS in the MIMO system. Thus, in such a case, it isdetermined that the received burst signal corresponds to a targetsystem. In this case, the demodulation unit 70 demodulates the targetdata which is assigned in a position posterior to the target LTS andtarget signal and is assigned in a channel corresponding to the targetsystem.

If, on the other hand, the detected at least two peaks are greater thanor equal to the threshold value, the decision unit 96 determines thatthe relation among a plurality of signal-wave components in the inputtedburst signal corresponds to the relation in the target STS and/or targetLTS in the MIMO system. Thus, in such a case, it is determined that thereceived burst signal corresponds to the MIMO system. In this case, theinstruction unit 74 stops the operation of the baseband processing unit62 for the first MIMO data and second MIMO data which are assigned inpositions posterior to the target STS and target LTS and are assignedrespectively in a plurality of channels corresponding to the MIMOsystem.

An operation of the target receiving apparatus structured as above willnow be described. FIG. 12 is a flowchart showing a procedure ofreceiving operation by a target receiving apparatus 54. When the targetreceiving apparatus 54 receives a target STS and a target LTS (Y ofS50), the correlation processing unit 90 carries out correlationprocessing (S52). The peak detector 94 detects at least two peaks (S54).If the interval of peaks is greater than or equal to a threshold value(Y of S56), the instruction unit 74 acquire the data length from theMIMO signal (S58). Then a stoppage period is determined from theacquired data length (S60), and the instruction unit 74 stops theoperation of the baseband processing unit 62 (S62). If, on the otherhand, the interval of peaks is not greater than or equal to thethreshold value (N of S56), the demodulation unit 70 demodulates thetarget data (S64). If the target receiving apparatus 54 does not receivethe target STS and the target LTS (N of S50). The processing will beterminated.

According to the second embodiment, the relation among a plurality oftarget STSs or a plurality of target LTSs in the MIMO system differsfrom the relation in a plurality of signal-wave components contained inthe received target STSs and/or target LTSs in the target system, sothat the receiving apparatus can detect burst signals in the MIMOsystem, based on the relation in a plurality of signal-wave componentscontained in the received signals. Since the operation of receiving isstopped when detected, the increase in power consumption can besuppressed. Since inspecting the header portion of a burst signal candecide on whether it is the burst signal in the MIMO system or not, theoperation can be stopped in a remaining part of the burst signal. Thusthe effect of reducing the power consumed will be significant. Since thetarget STSs and so forth transmitted from a plurality of antennas aresuch that their signal timings are mutually shifted, the correlationamong signals transmitted from a plurality of transmitting antennas canbe made small. Furthermore, the burst signal in a MIMO system can bedetected based on the correlation processing.

Third Embodiment

Similarly to the first and second embodiments, a third embodiment of thepresent invention relates to a receiving apparatus that receives a burstsignal from a transmitting apparatus corresponding to a target systemand a transmitting apparatus corresponding to a MIMO system and keepsreceiving the burst signal when the burst signal corresponds to thetarget system and stops receiving the burst signal when the burst signalcorresponds to the MIMO system. The receiving apparatus utilizes thephase of pilot signals to determine whether the received burst signalcorresponds to the target system or the MIMO system. The pilot signalsare assigned to predetermined subcarriers of a plurality of subcarriersused by the target system.

Pilot signals are known signals, which are referred to when a receivingapparatus estimates a radio channel. Even in a MIMO system; pilotsignals are assigned to subcarriers which correspond to the samefrequencies as those of the subcarriers to which the pilot signals areassigned in the target system (hereinbelow, pilot signals in a targetsystem will be referred to as “target pilot signals”, and pilot signalsin a MIMO system as “MIMO pilot signals”.) The target pilot signals andthe MIMO pilot signals are so defined as to have the same signal pointconstellation. However, the signal points of a target pilot signal andthose of a MIMO pilot signal corresponding to the same frequency are sodefined as to have different phases, such as inverted phases. Thereceiving apparatus extracts pilot signals from a received burst signaland determines whether the received burst signal corresponds to thetarget system or the MIMO system, based on the phase of the extractedpilot signals. That is, a decision is made using the phase of the pilotsignals.

The structure of a target receiving apparatus 54 according to the thirdembodiment is of the same type as that shown in FIG. 6. The judgmentunit 72 of the third embodiment, similarly to that of the firstembodiment, determines whether target data is assigned or a MIMO signalis assigned in a position posterior to the target signal. In the thirdembodiment, however, the relationship between the signal pointconstellation of the target data and the signal point constellation ofthe MIMO signal is different from that of the first embodiment. A signalthat is inputted to the target receiving apparatus 54 has a format asdescribed below.

As shown in FIG. 1, the target data and the MIMO signal are so definedas to use a plurality of subcarriers. 53 subcarriers, namely, subcarriernumbers “−26” to “26”, are used. Of a plurality of subcarriers used forthe target data and a plurality of subcarriers used for the MIMO signal,pilot signals are allotted to the mutually corresponding subcarriersthereof. In the standard of IEEE802.11a, pilot signals are assigned tothe subcarrier numbers “−21”, “−7”, “7” and “21”. In other words, aplurality of pilot signals are used.

The signal points in a target pilot signal and the signal points in aMIMO pilot signal have the same signal point constellation. The samesignal point constellation, as shown in FIG. 7B, is so defined that thein-phase component is “1” or “−1” while maintaining being compatiblewith BPSK. However, the signal points in a target pilot signal and thosein a MIMO pilot signal are so defined as to have mutually differentphases in the same subcarriers. For example, for the subcarrier number“−21”, the target pilot signal has the value of “1” whereas the MIMOpilot signal has the value of “−1”. In terms of the phases of FIG. 7B,the target pilot signal has the phase value of “0” whereas the MIMOpilot signal has the phase value of “π”.

In other words, there is an inverted relationship between the phase ofthe target pilot signal and that of the MIMO pilot signal correspondingto the same subcarrier. Arranged in order from subcarrier number “−26”to subcarrier number “26”, the target pilot signals have the values asshown in Equation (1) below. Here, “0” represents the absence ofassignment of a pilot signal.P_(−26,26)={0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,−1,0,0,0,0,0}  (1)

Similarly, on the other hand, the MIMO pilot signals have the values asshown in Equation (2) below.P′_(−26,26)={0,0,0,0,0,−1,0,0,0,0,0,0,0,0,0,0,0,0,0,−1,0,0,0,0,0,0,0,0,0,0,0,0,−1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0}  (2)

FIG. 13 illustrates a structure of a judgment unit 72 according to thethird embodiment. The judgment unit 72 includes a pilot signalextraction unit 110, a determination unit 112, a decision unit 84 and acondition storage 86.

The pilot signal extraction unit 110 receives and inputs demodulatedsignals from a demodulation unit 70. The demodulated signals areinputted to the pilot signal extraction unit 110 in the order ofsubcarrier numbers in units of FFT points. That is, a signalcorresponding to subcarrier number “−26” is first inputted and finally asignal corresponding to subcarrier number “26” is inputted. Followingthis, a signal corresponding to subcarrier number “−26” in the next OFDMsymbol is inputted. The pilot signal extraction unit 110 extracts pilotsignals from these inputted signals. In other words, signalscorresponding to subcarrier numbers “−21”, “−7”, “7” and “21” areextracted.

The determination unit 112 determines the identity of pilot signalsextracted by the pilot signal extraction unit 110. The extracted pilotsignals are primarily in possession of signal points as shown in FIG.7B. Due to influences present in the radio channel, the extracted pilotsignals are usually deviant from the signal points as shown in FIG. 7B.The deviation from the signal points, however, is one somewhat reducedby the demodulation performed by the demodulation unit 70. Thedetermination unit 112, which defines the orthogonal axes as thresholdvalues, determines an extracted pilot signal to be “1” if it lies in thefirst or the fourth quadrant. The determination unit 112 determines anextracted pilot signal to be “−1” if it lies in the second or the thirdquadrant. Ideally speaking, therefore, if the extracted pilot signalsare target pilot signals, the pilot signals are determined to be “1”,“1”, “1” and “−1” in the order of subcarrier numbers.

The condition storage 86 holds values for MIMO pilot signals asreference for the pilot signals determined by the determination unit112. That is, the condition storage 86 holds the values of “−1”, “−1”,“−1” and “1” in the order of subcarrier numbers.

The decision unit 84 compares the pilot signals determined by thedetermination unit 112 with the conditions held in the condition storage86 and decides whether or not the pilot signals determined by thedetermination unit 112 are MIMO pilot signals. In other words, thedecision unit 84 decides whether the signal point constellation of thepilot signals determined by the determination unit 112 corresponds tothe signal point constellation of the MIMO pilot signals or not. Forexample, if the values of the pilot signals determined by thedetermination unit 112 are “−1”, “−1”, “−1” and “1”, then the decisionunit 84 decides that the pilot signals determined by the determinationunit 112 are the MIMO pilot signals.

If the values of the pilot signals determined by the determination unit112 are “1”, “1”, “1” and “−1”, the decision unit 84 decides that thepilot signals determined by the determination unit 112 are not the MIMOpilot signals. On the other hand, where only part of the four signalsare in agreement with the conditions, then the decision unit 84 may makea decision according to the number of signals in agreement. For example,if three of the four signals are in agreement, the decision unit 84 willdecide that the pilot signals determined by the determination unit 112are the MIMO pilot signals. Moreover, the decision unit 84 can make theabove decision, using pilot signals in a plurality of OFDM symbols.

FIG. 14 is a flowchart showing a judgment procedure at a judgment unit72. This flowchart corresponds to Step 12 and Step 14 in FIG. 9. Thepilot signal extraction unit 110 extracts pilot signals (S80). Thedetermination unit 112 examines and determines the pilot signals (S82).If the pilot signals thus determined correspond to the phases of theMIMO pilot signals (Y of S84), the decision unit 84 decides that theMIMO signal is assigned (S86). On the other hand, if the pilot signalsthus determined do not correspond to the phases of the MIMO pilotsignals (N of S84), the decision unit 84 decides that target data isassigned (S88).

A modification according to the third embodiment as described above isnow explained. This modification makes use of signal pointconstellations in subcarriers other than the pilot signals, among aplurality of subcarriers. Similarly to the arrangement alreadydescribed, the target data and the MIMO signals are both so defined asto use a plurality of subcarriers, and, in addition, the pilot signalsare assigned to the mutually corresponding subcarriers of the pluralityof subcarriers used for the target data and the plurality of subcarriersused for the MIMO signals.

In this modification, however, the signal points in the subcarriersother than pilot signals in the target data (hereinafter referred to as“target carriers”) and the signal points in the subcarriers other thanpilot signals in the MIMO signals (hereinafter referred to as “MIMOcarriers”) are so defined as to have different constellations.Accordingly, the target carriers and the MIMO carriers are equivalent tosubcarriers other than the subcarriers numbered “−21”, “−7”, “7” and“21”. Also, the signal point constellation of the target carrierscorresponds to FIG. 7B, whereas that of the MIMO carriers corresponds toFIG. 7A. That is, the signal point constellation of the target carriersand that of the MIMO carriers have a mutually orthogonal relationship.

FIG. 15 illustrates a structure of another judgment unit 72 according tothe third embodiment. The judgment unit 72 includes a pilot signalremoving unit 114, an I-component processing unit 80, a Q-componentprocessing unit 82, a decision unit 84 and a condition storage 86.

The pilot signal removing unit 114 receives and inputs demodulatedsignals from a demodulation unit 70. The demodulated signals areinputted to the pilot signal removing unit 114 in the order ofsubcarrier numbers in units of FFT points. That is, a signalcorresponding to subcarrier number “−26” is first inputted and finally asignal corresponding to subcarrier number “26” is inputted. Followingthis, a signal corresponding to subcarrier number “−26” in the next OFDMsymbol is inputted. The pilot signal removing unit 114 extractssubcarriers other than pilot signals from the inputted signals. In otherwords, subcarriers corresponding to those other than subcarrier numbers“−21”, “−7”, “7” and “21” are extracted.

The I-component processing unit 80, the Q-component processing unit 82and the decision unit 84 perform the same operations as illustrated inFIG. 8. For carriers other than pilot signals, the decision unit 84compares the values of in-phase component and the values of quadraturecomponent with their respective conditions stored in the conditionstorage 86. At this time, the sum may be calculated for each of thevalues of in-phase component and the values of quadrature component of aplurality of carriers, and the sum of in-phase components and the sum ofquadrature components may be compared with their respective conditionsstored in the condition storage 86. Also, the decision unit 84 maycompare the value of in-phase components with the value of quadraturecomponents and decide that target data is assigned if the value ofin-phase components is larger or that MIMO signal is assigned if thevalue of quadrature components is larger. In other words, the decisionunit 84 may make a decision based on relative values. Here, the decisionunit 84 decides that MIMO signal is assigned if the signal pointconstellation in the carriers other than pilot signals in the positionsposterior to the target signal corresponds to the signal pointconstellation in the MIMO carriers. In this modification, therefore, thesame processing as described in the third embodiment is performed on thesignals corresponding to subcarriers other than pilot signals of aplurality of subcarriers in order to decide whether the MIMO signal isassigned or not.

Another modification of the third embodiment is explained. Thismodification is equal to a combination of the third embodiment and themodification as described hereinbefore. In a similar manner to theaforementioned, the target data and the MIMO signal are so defined as touse a plurality of subcarriers as shown in FIG. 1. Also, of a pluralityof subcarriers used for the target data and a plurality of subcarriersused for the MIMO signal, pilot signals are assigned to the mutuallycorresponding subcarriers thereof. Further, the signal points in atarget pilot signal and the signal points in a MIMO pilot signal havethe same signal point constellation and at the same time are so definedas to have mutually different phases in the same subcarriers. Also, thesignal point constellation of target carriers and those of the MIMOcarriers have a mutually orthogonal relationship.

FIG. 16 illustrates a structure of still another judgment unit 72according to the third embodiment. The judgment unit 72 has a structurecombining the judgment unit 72 of FIG. 13 and the judgment unit 72 ofFIG. 15, and therefore the description thereof is omitted. It is to benoted, however, that the decision unit 84 makes a decision based on theresults of a decision formed by the decision unit 84 of FIG. 13 and adecision formed by the decision unit 84 of FIG. 15. It may be arrangedsuch that in the event there is disagreement between the two results ofjudgment, one of the results of judgment, as predetermined, be used.Also, the decision unit 84 may select to use one of the results ofjudgment which it assumes to be accurate.

For example, suppose that in the judgment by pilot signals, the MIMOsignal is judged to be assigned for all of the four pilot signals andthat in the judgment by signals other than pilot signals, the targetdata is judged to be assigned for 36 of 48 pilot signals. Then it isdefined that the accuracy of the former judgment is 100 percent and thatof the latter 75 percent. Accordingly, the decision unit 84 follows theformer result of judgment. That is, the result of judgment with a higherrate is selected by comparing the rate of the judgment made by use ofpilot signals and the rate of the judgment made by use of subcarriersother than pilot signals.

According to the third embodiment of the present invention, the presenceor absence of a MIMO signal can be judged by the phase differencebetween the target pilot signal and the MIMO pilot signal. Since thephases of the target pilot signal and the MIMO pilot signal are in aninverted relationship, the difference between the two can be judgedaccurately. Moreover, due to the inverted relationship of the phases ofthe target pilot signal and the MIMO pilot signal, the judgment of thedifference between the two can be made and passed at high speed. Theconstellation of signal points other than pilot signals may bearbitrary, which contributes to raising the freedom of design.

Furthermore, the presence or absence of a MIMO signal can be judged bythe difference in signal point constellation between the target carriersand the MIMO carriers. Besides, the judgment can be accurate because thesubcarriers other than pilot signals are many. Moreover, thesignal-point constellation of pilot signals may be arbitrary, whichraises the freedom of design. The signal point constellation of the MIMOpilot signal can be the same as that of the target pilot signal, andtherefore the same signal point constellation can be applied and usedeven when the same pilot signals are defined for both the MIMO systemand target system. The presence or absence of a MIMO signal can bejudged by using the difference in phase between the target pilot signaland the MIMO pilot signal and the difference in signal pointconstellation between the target carriers and the MIMO carriers. Thejudgment can be accurate because it is based on a large number ofsignals.

The present invention has been described based on the embodiments whichare only exemplary. It is therefore understood by those skilled in theart that other various modifications to the combination of eachcomponent and process described above are possible and that suchmodifications are also within the scope of the present invention.

In the first to third embodiments of the present invention, theinstruction unit 74 extracts from the MIMO signal the lengths of thefirst MIMO-data and the like assigned respectively to a plurality ofchannels associated with a MIMO system. The arrangement is not limitedthereto, however. For example, the instruction unit 74 may use a targetsignal, which is assigned to a position prior to the MIMO signal. Thatis, the instruction unit 74 may extract from the target signal thelength of MIMO-data assigned respectively to a plurality of channelsassociated with the MIMO system and stop the operation of the basebandprocessing unit 62 for a period corresponding to the length of extractedMIMO-data. According to the present modifications, however, the lengthsof the first MIMO-data and the like may be extracted with a timingearlier than the MIMO signal. This can be done if the period forstopping the baseband processing unit 62 is known.

According to the second embodiment of the present invention, thedecision unit 96 decides whether a received signal is a burst signal ina MIMO system or not, based on the relationship between a plurality ofsignal-wave components contained in the received signal. The arrangementis not limited thereto, however. For example, as with the case in thefirst embodiment, it may be decided whether the MIMO signal is presentor not, based on the relationship between a plurality of signal-wavecomponents. In this case, the judgment unit 72 specifies therelationship between a plurality of signal-wave components contained inthe received target STS and/or target LTS and judges whether a MIMOsignal is assigned or not, based on the specified relationship and therelationship between the target STS and target LTS in the MIMO system.In this arrangement, the MIMO signal and the MIMO signal+CDD areassigned as shown in FIG. 10. The peak detector 94 derives at least twopeaks corresponding to the relationship and decides that a MIMO signalis assigned if the interval between the at least two peaks derived isgreater than or equal to a threshold value. According to the presentmodification, the criteria for deciding whether a MIMO signal is presentor not may be a combination of the above-mentioned criteria and thecriteria discussed in the first embodiment. This means that the accuracyof judgment on the presence of a MIMO signal can be improved by the useof a plurality of criteria. Which means the arrangement works if it isknown whether the MIMO signal is assigned or not.

In the first to third embodiments of the present invention, it has beenassumed that the target system is a wireless LAN in compliance with theIEEE802.11a standard. However, the arrangement is not limited theretobut can rely on another communication system, for instance. In suchmodifications as above, the present invention can be applied to avariety of communication systems. That is, such an arrangement issatisfactory if the target system and the MIMO system have a differenceof whether MIMO is applied or not and, in addition, the control signalin the MIMO system has the format of the channel of the target system.

In the first embodiment of the present invention, the judgment unit 72judges whether a MIMO signal is included in a burst signal or not.However, the arrangement is not limited thereto, but may be such thatone bit of the target signal shows a correspondence to the target systemor to the MIMO system and the judgment unit 72 detects said bit anddecides on the corresponding system from the detected bit. The presentmodifications simplify the processing. That is, such an arrangementworks if the system corresponding to the burst signal is known.

It will be obvious to those skilled in the art that a combination of allor part of the first to third embodiments works effectively. The presentmodifications produce a combined effect thereof.

While the preferred embodiments of the present invention have beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the appendedclaims.

1. A transmitting apparatus for transmitting an OFDM signal, comprising:a generator operative to generate a burst signal having a first burstformat where a first Non-MIMO training signal, a first Non-MIMO signal,a MIMO signal, a MIMO training signal, and first data are arranged inthe stated order; and a transmitter operative to transmit the burstsignal generated by the generator, wherein a subcarrier carrying a firstpilot signal included by frequency-division multiplexing in the firstdata in the first burst format of the burst signal generated by thegenerator is the same as a subcarrier carrying a second pilot signalincluded by frequency-division multiplexing in second data in a secondformat where a second Non-MIMO training signal, a second Non-MIMOsignal, and the second data are arranged in the stated order, amodulation scheme of the first pilot signal is the same as a modulationscheme of the second pilot signal, a pattern of the first pilot signalis different from a pattern of the second pilot signal, and thetransmitter transmits the burst signal from a plurality of antennas suchthat the signal transmitted from a given one antenna is shifted intiming with respect to the signal transmitted from another antenna in acyclical manner.
 2. A transmitting method for transmitting an OFDMsignal, comprising: generating a burst signal having a first burstformat where a first Non-MIMO training signal, a first Non-MIMO signal,a MIMO signal, a MIMO training signal, and first data are arranged inthe stated order; and transmitting the burst signal, wherein asubcarrier carrying a first pilot signal included by frequency-divisionmultiplexing in the first data in the first burst format is the same asa subcarrier carrying a second pilot signal included byfrequency-division multiplexing in second data in a second format wherea second Non-MIMO training signal, a second Non-MIMO signal, and thesecond data are arranged in the stated order, a modulation scheme of thefirst pilot signal is the same as a modulation scheme of the secondpilot signal, a pattern of the first pilot signal is different from apattern of the second pilot signal, and the transmitting transmits theburst signal from a plurality of antennas such that the signaltransmitted from a given one antenna is shifted in timing with respectto the signal transmitted from another antenna in a cyclical manner.